According to Return Path Inc.'s "Email Blocking and Filtering Report," for the first half of 2003, 17 percent of permission-based e-mail messages weren't delivered to recipients by the top ISPs. The e-mails were mistakenly tagged as spam. As ISPs and consumers use tougher spam filters, marketers who work hard to get permission to send messages will unfortunately see their response rates dwindle.

Marketers can help protect their e-mails from being inadvertently blocked. Permission-based e-mail marketing company e-Mail Networks Inc. offers a few tips to improve delivery success:

1. Watch the headers. Avoid sending e-mail to a large number of addresses in the "To", "CC" or "BCC" fields. If you use an e-mail system, make sure it sends one message at a time.

2. Craft subject lines with care. Write a subject line that shows it's from a trusted source. Avoid using words and symbols that can appear to be spam, such as "free," words in all caps or exclamation points.

3. Respond to e-mail requests. Instead of clicking an "unsubscribe" link, which should be included in your routine e-mail communications, subscribers may personally ask you to remove their addresses from your database. Do this immediately, and report the resolution to the recipients. Responding to their requests helps avoid a potential spam complaint, which could put you on ISPs' block lists.

4. Get added to "white lists." ISPs such as AOL and EarthLink allow subscribers to add e-mail addresses to their personal white lists. These lists specify the e-mail addresses allowed to pass through the ISP's spam filters. On your Web site page where visitors subscribe to e-mail communication from you, ask them to add your address to their white lists.

You may also want to include instructions for Internet users who are now using spam filters within their own e-mail programs, such as Microsoft Outlook. Users can add your company's e-mail address or domain name to their "safe senders" list.

5. Monitor your bounce rate. When specific e-mail addresses bounce back repeatedly, you can personally contact those individuals and ask to be added to their personal white lists. If you don't get a response, remove those e-mail addresses from your database. If you use an e-mail management system, find out if invalid e-mail addresses are removed for you. Too many bounced e-mails can trigger spam filters.

Also remember to post your privacy policy and unsubscribe instructions on your e-mail sign-up page. These assurances soothe your Web site visitors' concerns about getting secondary spam or being locked into your e-mail communication system forever. Not only will posting this information increase your opt-in rate, but if your company is investigated for a spam complaint, then it may help show that you're a permission-based company and not a spammer.